Were the nobles breaking a law of Moses?

Nehemiah 5 doesn't name one. Nehemiah's appeal is "Shouldn’t you walk in the fear of our God" (5:9), and the nobles answer without quoting any law (5:12). The Law does speak to these things, and these notes set its words beside the chapter without saying which one Nehemiah had in mind. On lending: "If you lend money to any of my people with you who is poor, you shall not be to him as a creditor. You shall not charge him interest" (Exodus 22:25); "You shall not lend on interest to your brother" (Deuteronomy 23:19); "Take no interest from him or profit; but fear your God, that your brother may live among you" (Leviticus 25:36). On a brother who is sold: "If your brother has grown poor among you, and sells himself to you, you shall not make him to serve as a slave" (Leviticus 25:39), "For they are my servants, whom I brought out of the land of Egypt. They shall not be sold as slaves" (Leviticus 25:42). On a poor brother: "you shall surely open your hand to him, and shall surely lend him sufficient for his need, which he lacks" (Deuteronomy 15:8). Two things are close to the chapter's own words. Leviticus 25:36 joins "fear your God" to the brother who may "live", and in Hebrew its verb live is the one in 5:2's "that we may eat and live". And later in the book the people's covenant promises to "forego the seventh year crops and the exaction of every debt" (Nehemiah 10:31), with the same Hebrew word as 5:7's and 5:10's usury (tap usury).